Wheat disease 5-15-15
(From left) Figure 1. Severe stripe rust on a wheat leaf in a research field at the ARDC near Mead on May 13. (Photo by Stephen Wegulo) Figure 2. Severe powdery mildew in the lower canopy in a wheat field in Lancaster County on May 14. (Photo by Tyler Williams) Figure 3. Septoria tritici blotch and powdery mildew in the lower canopy in a wheat field in Lancaster County on May 14. (Photo by Tyler Williams)
Severity of Wheat Diseases and Risk of Fusarium Head Blight Increasing
Weather conditions during the last two weeks (cool temperatures and moisture) have favored development of stripe rust which has been confirmed as far west as Perkins County. At the University of Nebraska Agricultural Research and Development Center (ARDC) near Mead on May 13, severity of stripe rust had increased to the extent that in some locations in a research field, entire leaves were yellow and covered with pustules (Figure 1).
Figure 4. A field in Cass County showing areas of yellow wheat without disease symptoms on May 14. (Photo by Tyler Williams)
Figure 5. Close-up of yellow wheat without disease symptoms (center and right) compared to wheat with normal green color (left). (Photo by Stephen Wegulo)
Severity of other wheat diseases favored by wet weather is also increasing. In a field surveyed in Lancaster County on May 14, powdery mildew (Figure 2) and Septoria tritici blotch (Figure 3) were severe in the lower canopy. This field also had stripe rust. In another field surveyed on May 14 in Cass County, there were areas within the field with yellow wheat that apparently was not diseased (Figure 4). This type of symptom (Figure 5) usually is associated with deficiency of certain nutrients in localized areas within a field.
Risk of Fusarium Head Blight
Frequent and heavy rains before and during flowering can significantly increase the risk of Fusarium head blight, a disease that bleaches heads of wheat and other small grain crops. Recent, current, and forecast weather conditions indicate that the risk of Fusarium head blight may be high this growing season especially in the eastern, south central, and southwestern parts of the state. In a growing season with favorable weather conditions, symptoms of Fusarium head blight start showing up in late May to early June.
Continue scouting wheat fields for diseases. Due to the current and forecast weather conditions which are favorable to disease development, a fungicide application is recommended to protect the flag leaf from stripe rust, powdery mildew, and leaf spot diseases such as Septoria tritici blotch and tan spot. The best timing for a fungicide application to suppress Fusarium head blight is at early flowering. A list of fungicides and their efficacies on wheat diseases is provided in a table developed by the North Central Regional Committee on Management of Small Grain Diseases (NCERA-184).
Extension Plant Pathologist